CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Steven E. Nissen, MD*
* Cleveland Clinic Foundation, Cardiovascular Medicine, 9500 Euclid Avenue, Desk F-15, Cleveland, Ohio 44195-0001 (Email: nissens{at}ccf.org).
The letter by Drs. Min and Berman proposes that, pending clinical effectiveness trials, "common sense should dictate clinical use" of computed tomography coronary angiography (CTCA). They further opine that "with its very high negative predictive value, an immediate benefit of the use of this test would be to eliminate the need for unnecessary invasive coronary angiography." In medicine, "common sense" has often been used to justify approaches to treatment that ultimately did not withstand careful scrutiny. Common sense suggested that use of antiarrhythmic agents to suppress premature ventricular contractions would benefit patients, when in fact such therapies produced the opposite result. "Common sense" is not a suitable alternative to rigorous clinical testing. In a second letter, Dr. Nicol and colleagues also emphasize a "negative predictive value in excess of 90%," which they state is unusual in medicine. These authors provide an explanation for the poor performance of CTCA in the Meijboom et al. (1) study, which they attribute to cut points used to define a "significant" stenosis.
In response, it must be noted that nuclear scintigraphy also has very high negative predictive value, exceeding 90% in multiple high-quality studies, accompanied by a more favorable positive predictive value. Both letters seem to miss the principal issues raised by the editorial (2). First, the high false-positive rate associated with CTCA represents a potential hazard to patients by stimulating unnecessary invasive angiography. The costs associated with false-positive studies are substantial, both in economic terms and through potential catheterization-related adverse outcomes, including morbidity from unnecessary interventions driven by the "oculostenotic reflex." Both sets of writers fail to acknowledge the substantial radiation burden imposed by CTCA and the potential to induce fatal malignancies, particularly in younger patients.
Even more importantly, the authors of both letters ignore the key premise underlying the editorial (2)—that it is not very useful to merely identify the presence or absence of stenoses. What clinicians need most is reliable information on the extent of inducible ischemia, data not provided by angiography. CTCA cannot replace current functional testing methods, because CTCA provides only limited anatomic information and does not reveal whether stenoses are clinically significant. Accordingly, clinicians must perform other diagnostic studies to determine whether the stenoses observed by CTCA are the likely cause of the patient's symptoms. Such serial testing is costly and inefficient. In a contemporary environment, where cost-effectiveness must be carefully considered, CTCA as currently employed represents a poor value compared with other diagnostic procedures.
Functional testing by stress echocardiography or nuclear scintigraphy provides greater clinical utility. In addition to identifying whether flow-limiting lesions are present, the exercise capacity and magnitude of the ischemic burden provide valuable prognostic information that can be used to guide therapy.
The burden of proof remains with the proponents of CTCA. They must demonstrate that this imaging modality provides superior value to existing diagnostic methods through meticulous comparative trials in which clinical performance and cost-effectiveness are rigorously measured. Until such studies are completed, CTCA should be viewed as a research tool and not a clinically proven diagnostic imaging modality.
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1. Meijboom WB, Meijs MF, Schiujf JD, et al. Diagnostic accuracy of 64-slice computed tomography coronary angiography: a prospective, multicenter, multivendor study J Am Coll Cardiol 2008;52:2135-2144.[Abstract/Free Full Text]2. Nissen SE. Limitations of computed tomography coronary angiography J Am Coll Cardiol 2008;52:2145-2147.[Free Full Text]
Related Article
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Placing Computed Tomography Coronary Angiography in Perspective
- James K. Min and Daniel S. Berman
J. Am. Coll. Cardiol. 2009 53: 1824.
[Full Text]
[PDF]
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